The width of the application field and therefore the importance of enzymes in modern technology is increasing rapidly. One of the major drawbacks of these compounds however, is their aptitude to deactivation, caused not only by extremes of temperature, pH and the like during processing, but also occurring spontaneously on prolonged storage under otherwise normal conditions.
Often applied methods known in the art to diminish this problem include the use of a variety of additives claimed to stabilize enzymes in solution or the conversion of the enzyme solution to a dry formulation by means of freeze drying, spray drying or other techniques suitable for this purpose. The conversion of an enzyme in solution to a dry form is often obligatory when the application so demands (e.g. convenient mixing with other dry components).
Although drying in itself is a valuable tool in the improvement of the enzyme storage stability, the process step itself often causes a substantial loss of activity and the final product is still susceptible to inactivation. This activity loss during storage or processing is strongly dependent on moisture content of the preparation and this therefore has to be most stringently controlled to maintain the so valued product stability. This also includes a severe reduction of choice in the compounds suited for addition to the final enzyme product for the sake of standardization or other purposes.
In a variety of cases the dry enzyme is intended for applications in which the enzyme has to be incorporated in a product in which the moisture content can not be so strictly controlled. In these cases the enzyme stability is then severely reduced.
Several inventions have been made in the field of stabilizing enzymes against losses during drying and subsequent storage and handling.
The bulk of these inventions (such as presented in the patent (applications) U.S. Pat. No. 3,515,642, EP 0501375A1 and WO 91/14773) are concerned with the addition of carbohydrate and, more specific, sugar or polyol components to the enzyme concentrate.
Also known in the art is the inclusion of components into the formulation with the aim to produce a glassy product at storage temperature, thus improving enzyme stability (EP 0383569A2).
Another approach is the addition to the formulation of one or several components able to bind moisture. This will reduce the water activity of the final preparation or temporarily prevent the interaction of water penetrating from the surroundings with the enzyme itself.
The use of organic and inorganic salts as a processing aid (e.g. to improve flowing behaviour of the product) or bulking/standardizing agent is well known. However, the use of inorganic salts to improve stability of dry enzyme preparations during processing or storage does not appear to be described in the art. In some cases enzyme destabilisation due to salt addition was even specifically mentioned (see e.g. Mikhailova et al. 1989, Vestsi Akad Navuk BSSR, Ser Biyal Navuk 6: 62-65).
EP 0522269A2 discloses the addition of insoluble calcium carbonate to an enzyme solution to be spraydried.
WO 92/11 347 discloses the incorporation of water soluble inorganic salts into enzyme containing granulates. The water soluble inorganic salts must be chosen such that they do not affect the storage stability of the enzyme granulate. WO 92/11347 provides several sodium- and potassium-salts as being suitable for this purpose. The water soluble inorganic salts are however added to the enzymes in dry form prior to their granulation by extrusion.